Articular cartilage has limited intrinsic healing capacity, and as a result, any injury, as well as the natural aging process, may lead to osteoarthritis (OA). Various reconstructive techniques are being employed for treatment of focal defects; however, there are few approaches being developed to address damage across cartilage surfaces with OA and to alter the progression of the disease. Although there are therapeutic molecules that may be of interest to treat OA, their systemic application is limited due to off-target concerns and local injection has limited efficacy due to short half-lives. To address these concerns, injectable hydrogels may be used to locally delivery and sustain the release of therapeutics to the joint. The objective of this study is to develop an injectable hydrogel for the delivery of therapeutic extracellular vesicles (EVs) and to evaluate the EV/hydrogel therapy in a minipig model of OA. Two Aims will be pursued towards this goal. In Aim 1 we will use our experience in biomaterial development to engineer a shear-thinning and self-healing hydrogel based on hyaluronic acid (HA). We will use dynamic covalent crosslinks to obtain these desired properties and will encapsulate and release EVs isolated from pig mesenchymal stromal cells (MSCs). The MSC EVs will be characterized for size, surface properties, and content before and after release and the release kinetics will be monitored with fluorescent labeling from hydrogels with a range of crosslink densities. This Aim will identify one hydrogel formulation that releases EVs over several weeks that can be used for in vivo assessment in Aim 2. In Aim 2 we will test the efficacy of our engineered hydrogel therapies in an in vivo setting. Using our Yucatan minipig model of OA, we will evaluate functional outcomes (histology, MRI) after injection of our hydrogels containing EVs. This evaluation will include activity measures (steps/day) and joint range of motion using custom motion tracking systems that we previously developed. Upon completion, we will have developed an injectable hydrogel therapeutic that is applied through a simple process similar to viscosupplements to deliver therapeutics to alter the progression of disease with OA. This therapy could be translated to the clinic for treatment of the large number of OA patients in the Veteran population who have few treatment options and could limit the number of total knee replacements performed.